This present invention relates to bicycle composite rims, and more particularly, to a bicycle composite rim having a three-dimensional reinforced hole and the method of manufacturing the composite bicycle rim.
A composite rim is made up of a plurality of fibrous sheets or plies that are cured within a bed of epoxy or resin. The fibers within the bed of epoxy or resin may be oriented in the X or Y directions and made of carbon, ceramic, glass or the like. Although fibers are very strong in their direction of orientation, they are less strong in their cross or perpendicular directions. Due to the anisotropic nature of fiber-reinforced composite sheets, the sheets oriented in the X-Y directions are reinforced by the fibers themselves, which can create and support load paths running along their length. However, in the sheet Z-direction, or out-of-plane direction, the fibers are only reinforced by the resin binding the sheets together. Further, the resin works best when it only has to transmit shear forces between sheets.
Problems arise in the area of through-holes on the rim because compression forces are concentrated at severed fiber ends at the through-hole edges, creating large tensile and shear forces in the resin itself. Ultimately, the high forces cause the resin to shear apart between the laminates, a failure mode known as interlaminar shear or delamination. This creates near infinite stress risers or concentrations at the crack edge between the plies of reinforcing fiber. Any subsequent loading causes the cracks to propagate very quickly. Ultimately, the sheet laminate loses its ability to withstand the compression loading and the laminate around the perimeter of the through-holes buckles. Accordingly, there is a need to provide a rim having 3-dimensional reinforced through-holes.